To determine the immune status of an individual has heretofore required a tedious, manual procedure involving incubating bacteria, complement and anti-sera in test tubes, plating a sample of the incubated mixture on a Petri dish, and counting the colonies which develop. In addition, due to the extreme variability of the assay, it is necessary to run replicates to obtain reliable results. This causes a considerable increase in the cost of the assay.